1. Technical Field
The present invention relates to a semiconductor device.
2. Related Art
A semiconductor element including GaN (gallium nitride) or SiC (Silicon carbide) has higher power conversion efficiency than a semiconductor element including Si (silicon). For example, a semiconductor device including GaN or SiC has a smaller amount of power loss than a semiconductor device including Si, and is therefore expected to realizing an energy saving effect. Conventionally, FETs (Field Effect Transistors) using GaN or SiC are provided with a cascode connection, as shown in Patent Documents 1 and 2, for example. Furthermore, FETs using SiC are provided in a cascade connection with FETs using Si, as shown in Patent Document 3, for example.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2010-522432    Patent Document 2: Japanese Patent Application Publication No. 2011-166673    Patent Document 3: Japanese Patent Application Publication No. 2014-3110
An IGBT (Insulated Gate Bipolar Transistor) using GaN or SiC is examined as a device that has a withstand voltage greater than or equal to 5 [kV] and a low ON voltage. In the IGBT using GaN or SiC, light having an energy of approximately 3 [eV], which is close to the bandgap energy of GaN or SiC, is generated inside the IGBT. Therefore, there is a problem that defects are caused in the gate insulating film of the IGBT due to the light with an energy of approximately 3 [eV]. Furthermore, there is a problem that this light with an energy of approximately 3 [eV] causes the charge trapped at a deep level in the gate insulating film to become excited and move to the channel region, thereby causing the gate threshold voltage to fluctuate from the predetermined value.